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<tr><th colspan="5" align="center" valign="bottom">PostgreSQL 8.2.3 中文文档</th></tr>
<tr><td width="10%" align="left" valign="top"><a href="catalog-pg-aggregate.html" accesskey="P">后退</a></td><td width="10%" align="left" valign="top"><a href="catalogs.html">快退</a></td><td width="60%" align="center" valign="bottom">章43. 系统表</td><td width="10%" align="right" valign="top"><a href="catalogs.html">快进</a></td><td width="10%" align="right" valign="top"><a href="catalog-pg-amop.html" accesskey="N">前进</a></td></tr>
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<div class="SECT1"><h1 class="SECT1"><a name="CATALOG-PG-AM">43.3. <tt class="STRUCTNAME">pg_am</tt></a></h1><a name="AEN61861"></a>
<p><tt class="STRUCTNAME">pg_am</tt> 存储有关索引访问方法的信息。系统支持的每种索引访问方法都有一行。这个表的内容在<a href="indexam.html">章49</a>详细讨论。</p>
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<p><b>表43-3. <tt class="STRUCTNAME">pg_am</tt> 字段</b></p>
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<tr><th>名字</th><th>类型</th><th>引用</th><th>描述</th></tr>
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<tr><td><tt class="STRUCTFIELD">amname</tt></td><td><tt class="TYPE">name</tt></td><td>&nbsp;</td><td>访问方法的名字</td></tr>
<tr><td><tt class="STRUCTFIELD">amstrategies</tt></td><td><tt class="TYPE">int2</tt></td><td>&nbsp;</td><td>这个访问方法的操作符策略个数</td></tr>
<tr><td><tt class="STRUCTFIELD">amsupport</tt></td><td><tt class="TYPE">int2</tt></td><td>&nbsp;</td><td>这个访问方法的支持过程个数</td></tr>
<tr><td><tt class="STRUCTFIELD">amorderstrategy</tt></td><td><tt class="TYPE">int2</tt></td><td>&nbsp;</td><td>如果索引不提供排序顺序则为零，否则就是描述排序顺序的策略操作符个数</td></tr>
<tr><td><tt class="STRUCTFIELD">amcanunique</tt></td><td><tt class="TYPE">bool</tt></td><td>&nbsp;</td><td>这种访问方式是否支持唯一索引?</td></tr>
<tr><td><tt class="STRUCTFIELD">amcanmulticol</tt></td><td><tt class="TYPE">bool</tt></td><td>&nbsp;</td><td>这种访问方式是否支持多字段索引?</td></tr>
<tr><td><tt class="STRUCTFIELD">amoptionalkey</tt></td><td><tt class="TYPE">bool</tt></td><td>&nbsp;</td><td>这个访问访法支持在一个索引字段上没有任何约束的扫描吗?</td></tr>
<tr><td><tt class="STRUCTFIELD">amindexnulls</tt></td><td><tt class="TYPE">bool</tt></td><td>&nbsp;</td><td>这种访问方式是否支持 NULL 索引记录?</td></tr>
<tr><td><tt class="STRUCTFIELD">amstorage</tt></td><td><tt class="TYPE">bool</tt></td><td>&nbsp;</td><td>允许索引存储的数据类型与列的数据类型不同?</td></tr>
<tr><td><tt class="STRUCTFIELD">amclusterable</tt></td><td><tt class="TYPE">bool</tt></td><td>&nbsp;</td><td>允许在一个这种类型的索引上群集?</td></tr>
<tr><td><tt class="STRUCTFIELD">aminsert</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>"插入这个行"函数</td></tr>
<tr><td><tt class="STRUCTFIELD">ambeginscan</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>"开始新扫描"函数</td></tr>
<tr><td><tt class="STRUCTFIELD">amgettuple</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>"下一个有效行"函数</td></tr>
<tr><td><tt class="STRUCTFIELD">amgetmulti</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>"抓取多个行"函数</td></tr>
<tr><td><tt class="STRUCTFIELD">amrescan</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>"重新开始这个扫描"函数</td></tr>
<tr><td><tt class="STRUCTFIELD">amendscan</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>"结束这次扫描"函数</td></tr>
<tr><td><tt class="STRUCTFIELD">ammarkpos</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>"标记当前扫描位置"函数</td></tr>
<tr><td><tt class="STRUCTFIELD">amrestrpos</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>"恢复已标记的扫描位置"函数</td></tr>
<tr><td><tt class="STRUCTFIELD">ambuild</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>"建立新索引"函数</td></tr>
<tr><td><tt class="STRUCTFIELD">ambulkdelete</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>批量删除函数</td></tr>
<tr><td><tt class="STRUCTFIELD">amvacuumcleanup</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td><tt class="COMMAND">VACUUM</tt> 后的清理函数</td></tr>
<tr><td><tt class="STRUCTFIELD">amcostestimate</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>估计一个索引扫描开销的函数</td></tr>
<tr><td><tt class="STRUCTFIELD">amoptions</tt></td><td><tt class="TYPE">regproc</tt></td><td><tt class="LITERAL"><a href="catalog-pg-proc.html"><tt class="STRUCTNAME">pg_proc</tt></a>.oid</tt></td><td>为一个索引分析和确认 <tt class="STRUCTFIELD">reloptions</tt> 的函数</td></tr>
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<tr><td width="33%" align="left" valign="top"><a href="catalog-pg-aggregate.html" accesskey="P">后退</a></td><td width="34%" align="center" valign="top"><a href="index.html" accesskey="H">首页</a></td><td width="33%" align="right" valign="top"><a href="catalog-pg-amop.html" accesskey="N">前进</a></td></tr>
<tr><td width="33%" align="left" valign="top"><tt class="STRUCTNAME">pg_aggregate</tt></td><td width="34%" align="center" valign="top"><a href="catalogs.html" accesskey="U">上一级</a></td><td width="33%" align="right" valign="top"><tt class="STRUCTNAME">pg_amop</tt></td></tr>
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